Endoscopic surgical instruments are often preferred over traditional open surgical devices since a smaller incision tends to reduce the post-operative recovery time and complications. Consequently, significant development has gone into a range of endoscopic surgical instruments that are suitable for precise placement of a distal end effector at a desired surgical site through a cannula of a trocar. These distal end effectors engage the tissue in a number of ways to achieve a diagnostic or therapeutic effect (e.g., endocutter, grasper, cutter, staplers, clip applier, access device, drug/gene therapy delivery device, and energy device using ultrasound, RF, laser, etc.).
Known surgical staplers include an end effector that simultaneously makes a longitudinal incision in tissue and applies lines of staples on opposing sides of the incision. The end effector includes a pair of cooperating jaw members that, if the instrument is intended for endoscopic or laparoscopic applications, are capable of passing through a cannula passageway. One of the jaw members receives a staple cartridge having at least two laterally spaced rows of staples. The other jaw member defines an anvil having staple-forming pockets aligned with the rows of staples in the cartridge. The instrument includes a plurality of reciprocating wedges which, when driven distally, pass through openings in the staple cartridge and engage drivers supporting the staples to effect the firing of the staples toward the anvil.
An example of a surgical stapler suitable for endoscopic applications is described in U.S. Pat. No. 5,465,895, which advantageously provides distinct closing and firing actions. Thereby, a clinician is able to close the jaw members upon tissue to position the tissue prior to firing. Once the clinician has determined that the jaw members are properly gripping tissue, the clinician can then fire the surgical stapler with a single firing stroke, thereby severing and stapling the tissue. The simultaneous severing and stapling avoids complications that may arise when performing such actions sequentially with different surgical tools that respectively only sever or staple.
One specific advantage of being able to close upon tissue before firing is that the clinician is able to verify via an endoscope that the desired location for the cut has been achieved, including that a sufficient amount of tissue has been captured between opposing jaws. Otherwise, opposing jaws may be drawn too close together, especially pinching at their distal ends, and thus not effectively forming closed staples in the severed tissue. At the other extreme, an excessive amount of clamped tissue may cause binding and an incomplete firing.
Generally, a single closing stroke followed by a single firing stroke is a convenient and efficient way to perform severing and stapling. However, in some instances, it would be desirable for multiple firing strokes to be required. For example, surgeons are able to select a length of staple cartridge for the desired length of cut from a range of jaw sizes. Longer staple cartridges require a longer firing stroke. Thus, to effect the firing, a hand-squeezed trigger is required to exert a larger force for these longer staple cartridges in order to sever more tissue and drive more staples as compared to a shorter staple cartridge. It would be desirable for the amount of force to be lower and comparable to shorter cartridges so as not to exceed the hand strength of some surgeons. In addition, some surgeons, not familiar with the larger staple cartridges, may become concerned that binding or other malfunction has occurred when an unexpectedly higher force is required.
One approach for lowering the required force for a firing stroke is a ratcheting mechanism that allows a firing trigger to be stroked multiple times, as described in U.S. Pat. Nos. 5,762,256 and 6,330,965. These known surgical stapling instruments with multiple-stroke firing mechanisms do not have the advantages of a separate closure and firing action. Moreover, the ratcheting mechanism relies upon a toothed rack and driving pawl to achieve the ratcheting motion, with the length of a handle encompassing these components thus increased to accommodate the toothed rack. This increased length is inconvenient, given the close confines and increasing amount of equipment associated with a surgical procedure.
While these multiple firing strokes would have advantages, some features of a single firing stroke have advantages as well. For instance, a single-stroke firing trigger may be directly coupled to the firing mechanism even during release of the firing trigger. Thus, any spring bias on the single-stroke firing trigger assists in retracting the knife from the end effector. If binding occurs, the surgeon may urge the firing trigger outward to effect retraction since the firing trigger is directly coupled to the firing mechanism.
By contrast, the multiple-stroke firing trigger is uncoupled from the firing mechanism during return strokes. While a retraction bias force is advantageously incorporated to retract the knife from the staple applying assembly, this retraction force needs to be prevented from performing retraction of the knife before full firing travel is achieved.
Consequently, a significant need exists for a surgical stapling instrument having a multiple stroke firing mechanism that automatically retracts after full firing travel yet does not inadvertently retract between firing strokes.